The invention relates to an AC generator for use in motor vehicles, which is capable of generating high power voltage, and which is high in both power generation efficiency and cooling efficiency.
FIG. 1 is a sectional view showing a conventional AC generator for use in motor vehicles. In FIG. 1, reference numeral 31 designates a stator core; 32, a stator coil wound around the stator core 31; 3, a stator including the stator core 31 and the stator coil 32; 1 and 2, a pair of first and second generally bowl-like brackets; 1a and 2a, cooling air inlets disposed at ends of the first and second brackets 1 and 2; 1b and 2b, cooling air outlets disposed at outer peripheral portions of the first and second brackets 1 and 2; 20, a bolt for clamping and securing the stator core 3 between opening ends of the first and second brackets 1 and 2 by inserting the opening ends to both outer peripheral end portions of the stator core 31; 4 and 5, bearings firmly inserted into the middle of both side surfaces of the first and second brackets 1 and 2; 6, a shaft rotatably supported on the bearings 4 and 5; 7 and 8, magnetic cores secured to the shaft 6 and located inside the stator 3; 9, an exciting coil (not shown) interposed between the inner peripheries of the magnetic cores 7 and 8; 10a and 10b, a pair of fans which are secured to end surfaces of the magnetic cores 7 and 8 the fans rotating as the shaft 6 rotates; 11, a slip ring secured to the shaft 6; 12, a rotor including of the shaft 6, the magnetic cores 7 and 8, the exciting coil 9, the fans 10a and 10b, and the slip ring 11; 13, a collector unit holding a brush 13a which is in slidable contact with the slip ring 11 and disposed at an inner end surface of the second bracket 12; 14, a rectifier which converts an AC current to a DC current by rectifying the AC current while supplying exciting current to the exciting coil 9 through the slip ring 11 from the brush 13a and rectifying the AC current induced at the stator coil 32 by causing the magnetic cores 7 and 8 to be rotated by a prime mover (not shown) through a pulley 15; 16, a voltage adjustor which adjust a terminal voltage to a predetermined value by controlling the exciting current while detecting a generator voltage; and 16a, a heat sink for releasing heat generated at the voltage adjustor 16.
FIG. 2 is a schematic diagram showing the stator 3 for a description of the magnetic circuit configuration and winding system of the conventional AC generator applied to vehicles. Shown in FIG. 2 is a 3-phase, 12-pole, 36-slot configuration with the number of slots per each pole and each phase, which represents the number of slots per the product of the number of poles and the number of phases is 1. The three phases are designated by phase A, phase B and phase C. Reference numeral 32a designates a coil for phase A; 32b, a coil for phase B; and 32c, a coil for phase C. Reference numerals 31a, 31b , 31c, 31d, 31e, 31f, and 31g designate tooth portions constituting part of a magnetic path of the stator core 31, while 7a and 8a, 8b designate claw magnetic poles which confront the tooth portions and which constitute the magnetic cores 7, 8. Assuming that the claw magnetic pole 7a is magnetized into an N pole, each of the claw magnetic poles 8a, 8b is magnetized into an S pole.
An operation of the conventional AC generator applied to vehicles will be described.
The exciting coil 9 is supplied with exciting current through the brush 13a and the slip ring 11, thereby causing the claw magnetic pole 7a to be magnetized as an N pole and each of the claw magnetic poles 8a and 8b as an S pole. A magnetic flux .phi. passes from the N pole of the claw magnetic pole 7a to the claw magnetic poles 8a and 8b through the tooth portions 31a, 31b and 31c of the stator core 31. Since the coil 32a of phase A is wound around the tooth portions 31a, 31b and 31c, the coil 32a of phase A intersects the magnetic flux .phi. passing through the tooth portions 31a, 31b and 31c, and the movement of the claw magnetic poles 7a, 8a and 8b in the direction of an arrow z causes the magnitude and direction of the intersecting flux .phi. to change. As a result, a change in the intersecting flux .phi. generates an inductive electromotive force (EMF) at the coil 32a of phase A. Since the tooth portions 31a, 31b and 31c alternately confront the N and S poles, an AC EMF is induced at the coil 32a of phase A. Similarly, AC EMFs are induced at the coils 32b and 32c of phases B and C, respectively. A total of 6 coils are connected to each of phases A, B and C in series, and the AC EMFs induced at these phases are superposed on one another, generating AC current. This AC current is rectified by the rectifier 14 to be outputted as a DC current. The output voltage is adjusted to a constant value by the voltage adjustor 16.
A cooling structure will be described hereinafter.
When the rotor 12 is rotated by a drive mechanism (not shown) through the pulley 15, the fans 10a and 10b secured to the rotor 12 start rotating to allow a cooling air from the inlet 1a of the first bracket 1 as shown by the arrow (a) shown in FIG. 1. After cooling the bearing 4, the magnetic core 7, the exciting coil 9, the stator core 31 and the stator coil 32, the cooling air is discharged outside from the outlet 1b. Simultaneously, the cooling air is introduced from the inlet 2a of the bracket 2 as shown by arrow (b) to cool the bearing 5, the voltage adjustor 16, the rectifier 14, the magnetic core 8, the magnetic coil 9, the stator core 31 and the stator coil 32 and discharged from the outlet 2b.
The conventional AC generator equipped to motor vehicles is constructed as above. However, to meet the recent demand for particularly large output current, such a conventional AC generator is required to increase an exciting current. This results in an increase in heat generated by the voltage adjustor 16 and also in an increase in heat generated by the stator coil 32 and the rectifier 14 due to increased output current.
Particularly, the increase in heat generated at the stator coil 32 has so far been taken care of by decreasing its resistance while increasing the diameter of its conductor. However, there is a limit in increasing the conductor diameter in view of winding work. In addition, the demand for higher output current and smaller structure may eventually lead to impairment of generation characteristics due to heat resistance limitations. The invention has been accomplished in view of the above circumstances.